This invention relates generally to tensioners, which can be used with chain drives in automotive timing and power transmission applications, and, more particularly, to blade-type chain tensioners, with a vibration damping feature.
Chain tensioning devices are used to control power transmission chains as the chain travels between a set of sprockets. Such chains usually have at least two separate strands, spans or lengths extending between the drive sprocket, such as a crankshaft sprocket, and the driven sprocket, such as a cam sprocket. The strand between the sprockets where the chain leaves the driven sprocket and enters the drive sprocket is frequently under tension as a result of the force imposed on the chain by the drive sprocket. The strand between the sprockets where the chain leaves the drive sprocket and enters the driven sprocket is frequently under reduced drive tension or slack due to the absence of driving force exerted on that strand. In systems with large center distances between the sprockets, both strands may evidence slack between the sprockets.
As a consequence, it is essential to the proper operation of the chain and sprocket system that a proper degree of engagement between the chain members and the sprockets is maintained during operation of the system. One aspect of maintaining such engagement of chain and sprocket is maintaining a proper degree of tension in the chain strands. The loss of chain tension can cause undesirable vibration and noise in the chain strands. The loss of chain tension also increases the possibility of chain slippage or unmeshing from the teeth of the sprocket, reducing engine efficiency and, in some instances, causing system failures. For example, it is especially important to prevent the chain from slipping in the case of a chain-driven camshaft in an internal combustion engine because misalignment of camshaft timing by several degrees can render the engine inoperative or cause damage to the engine.
The tension of the chain can vary due to wide variations in temperature and linear expansions among the various parts of an engine. Moreover, wear to the chain components during prolonged use also may produce a decrease in the chain tension. In addition, the intermittent stress placed on the chain devices in automotive applications due to variation in engine speed, engine load and other stress inducing occurrences can cause temporary and permanent chain tension.
To maintain tension in such transmission systems, tensioner devices have been used to push a tensioner member against the chain along a chain strand. Such transmission systems, typically press on the chain effective to mechanically deflect the strand path and impart the desired degree of tension on the chain. Current tensioner devices for performing this function include blade spring tensioners, which utilize one or more arcuate blade springs interlocked under tension with a relatively flat shoe made of plastic. The blade spring tensioner operates by permitting the chain to run across the plastic shoe. The spring blade(s) that is inserted within the shoe causes the shoe to creep or deform to a more arcuate shape as the shoe is heated, for example, from the contact of the shoe being driven across its surface. For example, U.S. Pat. No. 3,490,302 discloses such a chain tensioner where the blade spring is mounted to mechanically interlock with a shoe through a hole and pin combination. U.S. Pat. No. 4,921,472 discloses a blade spring tensioner having blade spring mechanically interlocked with a shoe through a passageway in the end of the shoe without the use of a pin. U.S. Pat. No. 5,266,066 discloses another blade spring chain tensioner in which a blade spring is constructed from a simple rectangular metal band formed in an arcuate shape and interlocked with a pocket in a shoe to provide a load to the shoe.
Unfortunately, the prior blade-type tensioners have certain drawbacks. For one, they are prone to prolonging oscillation of the chain. The harsh operating conditions of the engine induces varying tension in the chain. For instance, the cam shaft and crank shaft may induce torsional vibrations which cause chain tension to vary considerably. Moreover, abrupt tension variations may cause the chain to elongate in accordance with the chain stiffness. The blade spring reacts to the varying tension in the chain imparted by the torsional vibrations. Depending on the vibrational frequency, the spring force of the blade spring may react with a resonant vibration that establishes a prolonged oscillation of the chain. It is desirable to neutralize these inadvertent oscillations in the chain tensioning system as soon as possible and maintain a constant tension on the chain.
As one prior approach for addressing this oscillation problem, at least under certain limited conditions, U.S. Pat. No. 5,462,493 discloses a dual blade spring tensioner constructed of a pair of shoes in which one shoe is adapted to impart tension to a chain and overlaps the other shoe which is connected to a blade spring. The dual blade spring tensioner creates a passive mechanical damping feature by using the overlapping shoes to damp chain oscillations and vertical vibrations.
Despite these advances, the prior blade spring tensioning systems generally have found their applications limited to chain tensioning systems involving relatively short chain strands and low dynamic loads. More particularly, the prior blade spring tensioners generally have not performed as desired or needed on tensioning systems involving long strands or high dynamic loads, as they lack sufficient damping capability and/or offer inadequate tension control at system resonance in those more challenging environments for chain tensioning. Timing chains are subject to periodic tension inducement events in the engine, such as not only sprockets engaging the chain but also torque and cam engine vibrations transmitted through the engine block. The multiple forces acting on the tensioning system may accumulate or cancel, although some net vibrational frequency can and often does occur.
As a consequence, in chain tensioning systems involving long strands and/or high dynamic loads, hydraulic chain tensioner devices have been considered and used to provide dual functions of maintaining constant chain tension and dampening of chain movement. A hydraulic tensioner typically has a plunger slidably fitted into a chamber and biased outward by a spring to provide tension to the chain. Hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through a check valve and passages formed in the housing of the device. The plunger may move outward against the chain, directly against a tensioner arm principally by an internal spring or similar structure and the plunger position is maintained in large part by hydraulic pressure within the housing. Such a hydraulic tensioner as used with a tensioner arm or shoe is shown in U.S. Pat. No. 5,967,921.
Regarding the mechanics of vibration damping with use of a hydraulic chain tensioner, as a chain traverses its path, it may vibrate or xe2x80x9ckickxe2x80x9d causing the chain to push against the tensioner arm. The force of the vibration or kick is transferred to the tensioner device causing the hydraulic plunger to move in a reverse direction away from the chain. This reverse movement is resisted by the hydraulic fluid in the chamber, as flow of the fluid out of the chamber is restricted by the check valve assembly. In this fashion, the tensioner achieves a so-called no-return function, i.e., movements of the plunger are relatively easy in one direction (toward the chain) but difficult in the reverse direction. In addition, rack and ratchet assemblies also may be employed to provide a mechanical no-return function.
Unfortunately, the hydraulic tensioners can be relatively expensive in comparison to conventional blade spring type chain tensioners. In addition, in some applications, the size and bulk of prior hydraulic tensioners can present difficulties in mounting and operating such tensioners. To overcome the difficulty created by the size of prior hydraulic tensioners, lever systems have been employed that allow the mounting of the hydraulic tensioner at a distance from the chain assembly. Through the lever system, the hydraulic tensioner imparts pressure on one or more strands of the chain assembly thereby maintaining chain tension. However, such lever mechanisms add to the complexity of the tensioner system and involve additional moving parts with a concomitant increase in maintenance expenses, problems and equipment failures. The use of such pivoted lever mechanisms may also diminish the ability of the hydraulic tensioners to dampen chain vibration. In addition, the mechanical limitations of the typical rod and piston design of hydraulic tensioners may limit the amount of slack which can be taken up by the tensioner during the life of the chain.
The use of piezoelectric materials has been proposed and implemented in some specific applications involving vibrational or acoustical damping, for example such as in skis, car body panels, noise attenuation in aircraft and vehicle operator/passenger cabins, washing machine panels, and aesthetic uses such as in LED xe2x80x9cflashing lightxe2x80x9d athletic sneakers. Piezoelectricity is a property of certain classes of crystalline xe2x80x9cpiezoelectricxe2x80x9d materials, including natural crystals of quartz, Rochelle salt and tourmaline, as well as manufactured ceramics, such as barium titanate and lead zirconate titanates (i.e., PZT). When mechanical pressure is applied to a piezoelectric material (e.g., by pressing, squeezing, stretching, etc.), the crystalline structure produces a voltage, which is proportional to the applied pressure. Conversely, when an electric field is applied, it is believed that the crystalline structure changes shape, thus producing dimensional changes in the material.
In most cases, the same element can be used to perform either task. For a positive voltage applied in the z-direction to a piezo material, a solid rectangular piece will expand in one direction (z) and contract in the other two (x and y); if the voltage is reversed, the piece will contract in the z-direction and expand in the x- and y-directions. Thus, piezo motors (i.e., actuators) convert electrical energy to mechanical energy, and piezo generators (i.e., sensors) convert mechanical energy into electrical energy. A bimorphic piezo actuator comprises two flat, thin layers of piezoelectric material permanently bonded together, back-to-back, and wired out-of-phase with one another. When one layer expands, the other layer contracts, causing the actuator to bend, much like a bi-metal strip.
Around 1995, Active Control Experts (ACX), of Cambridge, Mass., now a division of Cymer, Inc., utilized this double-layer piezoelectronic technology with a passive resonant circuit to reduce vibrations in skis, marketed as the K2 xe2x80x9cFourxe2x80x9d ski. The ACX devices dissipated mechanical energy as heat by first converting it to electricity and then passing it through a resistive shunt, in which a shunt circuit is tuned to damp only those vibratory modes that adversely affect ski performance. Piezoelectric actuators also have been provided with an active digital signal processing (DSP) control system for purposes of reducing random buffeting vibrations experienced in the tails of high-speed jet aircraft. The dissipation loads for these prior vibration systems are relatively low such that the shunt resistor circuit could tolerate the heat generated by dissipating a charge potential across a resistor. They did not involve high rpm dynamic mechanical systems and the like.
U.S. Pat. No. 5,458,222, entitled xe2x80x9cActive Vibration Control Of Structures Undergoing Bending Vibrations,xe2x80x9d discloses piezo transducers on panels, such as jet engine ducts or washing machine panels, piezo actuated by an AC signal to pre-stress a structure, such that bending vibrations are canceled.
U.S. Pat. No. 5,498,127, entitled xe2x80x9cActive Acoustic Liner,xe2x80x9d discloses a rigid backplate that supports a piezoelectric panel around an intake fan area, driven to reduce noise in a jet engine.
U.S. Pat. No. 5,812,684, entitled xe2x80x9cPassenger Compartment Noise Attenuation Apparatus For Use In A Motor Vehicle,xe2x80x9d discloses a piezoelectric sensor and piezoelectric actuator attached to a side glass of an automobile at points along a fundamental node of vibration, wherein the actuators are vibrated in reverse phase to a signal generated by the sensor.
U.S. Pat. No. 6,138,996, entitled xe2x80x9cVibration Control Device For Automotive Panels,xe2x80x9d discloses a piezoelectric element used to counteract a stress of the panel created by vibration, thereby effectively increasing the rigidity of the panel. Modules including a single electromechanical transducer are applied to one side of a car frame member, or alternatively sandwiched upon opposite sides of a panel member. The ""996 patent also discloses use of a resonant circuit to reduce vibration.
U.S. Pat. No. 6,178,246, entitled xe2x80x9cApparatus For The Active Suppression Of Noise Radiated By A Surface,xe2x80x9d discloses axially sensitive piezo noise sensors and a noise suppression actuator for a vehicle body wall. Further, U.S. Pat. Nos. 5,656,882, 5,687,462, and 5,857,694 disclose piezoelectric dampers that are suitable for numerous applications.
Blade spring tensioning systems for chains are typically used in highly dynamic systems such as moving power transmission and timing chains that bear against the surface of a blade spring and shoe assembly. The blade spring and shoe assembly is intended to be generally stationary in its equilibrium position, and to respond to and mitigate slack in the chain. Thus, the blade spring and shoe assembly often is subjected to significant forces during tensioning of the chain. Impacts and mechanical forces occur throughout the engine block, in addition to impacts associated with the chain and its sprocket engagements, and often are transmitted directly and indirectly from those sources and through the chain to the blade spring tensioner. Similar forces also are exerted on tensioners in other systems in dynamic and high stress environments. In many applications, such of these forces are recurrent at a constant vibrational frequency. For example, a timing chain may resonate at 5000 Hz when rotated at 5000 rpm. In many instances the associated vibrational energy is transmitted to the blade spring and shoe assembly, over time, can accelerate wear and reduce the durability of the blade tensioner system, the chain system, chain sprockets and associated system. Also, the desire in some instances to design vehicular engines with a smaller number of cylinders but operated at higher rpm, also possibly may contribute to increased chain vibration. The present invention provides vibration control effective to reduce such vibration in a blade tensioner.
According to the invention, a blade-type chain tensioner is provided including a shoe attachable to a support surface, a blade spring engaging the shoe, a piezoelectric strain actuator element operatively coupled to the blade spring and shoe assembly, and a circuit adapted to receive sensor signals generated by a sensor element coupled to the blade spring and shoe assembly, in which the circuit interacts with the piezoelectric strain actuator element to induce a vibratory moment therein effective to absorb and dissipate vibration in the chain tensioner when a sensor signal, received by the circuit, is associated with a vibration in the blade spring and shoe assembly occurring at a predetermined frequency or in predetermined frequency band. The damped blade-type chain tensioner of the present invention directly addresses the problem of chain-induced vibration in particular, as well as other vibration transmitted to the blade tensioner from other parts of the vehicle in general, to decrease wear or fatigue of the blade tensioner, thereby increasing its durability and thus extending its useful life.
In one general aspect of the present invention relating to a passive chain tensioner damping system, the circuit comprises a passive analog resonance circuit tuned to a predetermined resonance frequency or frequency band of a vibration of the blade spring and shoe assembly of the chain tensioner to be controlled. When vibration at the predetermined resonance frequency or frequency band occurs in the blade spring and shoe assembly, the mechanical stress or motion imparted to a sensor element coupled to the vibrating blade spring and shoe assembly is converted into a sensor signal supplied to the resonance circuit. In response to receiving a sensor signal associated with a blade spring or shoe vibrating at its predetermined resonance frequency or frequency band, the passive analog resonance circuit converts the vibrational mechanical energy into electric energy having a voltage, frequency and phase effective to induce a vibratory moment in the piezoelectric strain actuator element to which it is coupled, which counteracts and neutralizes the vibration in the blade spring and shoe assembly.
In one aspect of the passive damping embodiment of this invention, the sensor element comprises a piezoelectric transducer element attached to the blade spring or shoe that converts vibrational-induced stresses into electrical energy manifested as a voltage. When a predetermined resonant frequency or frequency band is of vibration occurs in the blade spring and shoe assembly, the voltage generated in the piezoelectric sensing element is inverted in phase by the passive analog resonance circuit and supplied back to a second piezoelectric transducer element that is mechanically coupled to the blade spring and shoe assembly. The second piezoelectric transducer element is used as a strain actuator element for conversion of the inverted voltage into a physical stress causing a physical deformation in the strain actuator element which counteracts and neutralizes the vibration of the blade spring and shoe assembly.
In general, the decision in tuning the passive analog resonance circuit to invert and supply voltage to the piezoelectric strain actuator element at either approximately a single frequency, or instead over a band of frequencies, takes into consideration a tradeoff between a higher efficiency damping and functional bandwidth (Q-factor). Ideally, the analog resonance circuit inverts the input sensor signal in phase and amplitude such that the output signal will have optimal efficiency in canceling out the resonant frequency in the blade spring and shoe assembly. Generally, the broader the frequency band tuned (filtered) for in the passive analog resonance circuit, the lower the damping efficiency (i.e., the absolute value of the amplitude of the inverted voltage becomes relatively lower relative to the sensed input voltage as a function of increasing bandwidth responsivity). The damping efficiency must be maintained high enough to permit reduction or cancellation of a resonant vibration in the blade spring and shoe assembly.
In another aspect of the invention, the piezoelectric strain actuating element and the piezoelectric transducer sensing element are generally discrete planar elements arranged in parallel to each other in an integral electromechanical piezoelectric transducer module coupled to a surface of the blade spring. In this configuration, the piezoelectric transducer sensing element generally, although not necessarily for all cases, is located closer to a surface of the blade spring or shoe, while the piezoelectric strain actuating element is attached on the side of the sensing element opposite to the blade spring or shoe. In this aspect, a vibratory moment induced into the piezoelectric strain actuating element directly counteracts resonant vibration occurring in the sensing element, which in turn, counteracts the resonant vibration in the blade spring or shoe to which the sensing element is in direct contact with. Alternatively, the piezoelectric transducer sensing element and the piezoelectric strain actuating element need not overlap with one another in a laminate form, but alternatively can be attached to different discrete locations along the surface of the blade spring or shoe suitable for resonant vibration counteraction. In one preferred aspect, the piezoelectric strain actuator element is coupled to the blade spring adjacent a point of predicted maximum deflection of the blade spring as expected during a vibration in the blade spring and shoe assembly at a predetermined resonant frequency or in a predetermined resonant frequency band.
The term xe2x80x9cadjacent,xe2x80x9d as used herein in the context of the location of the piezoelectric strain actuating element, encompasses its direct attachment to a blade spring or shoe surface, or an indirect attachment or coupling via an intervening sensing element as described herein or any intervening binder or transducer module encapsulating material, and so forth, as long as the vibratory moment generated in the actuating element such as described herein can still reduce the vibration in the blade spring and shoe assembly in accordance with a purpose of the invention.
In an alternative general aspect of the present invention, the damping system functions as an active chain tensioner damping system. In one aspect of operation using the active damping system, a piezoelectric transducer sensing element is coupled to the blade or shoe of the blade spring and shoe assembly. It is used to xe2x80x9csensexe2x80x9d the occurrence of a vibration of the blade spring or shoe (which also can be referred to as the xe2x80x9ctensioner bladexe2x80x9d), and generate a sensor signal indicating a characteristic (e.g., amplitude, frequency and/or phase) of the vibration in the blade spring and shoe assembly. A control unit includes active control logic comprising a microprocessor with mapping for processing the sensor signal supplied by the piezoelectric transducer sensing element and an active control circuit for determining the amplitude and frequency of the vibration detected in the blade spring and shoe assembly.
When a predetermined frequency or frequency band of vibration in the spring blade and shoe assembly is detected by the control unit, the active control circuit produces electric energy having a voltage, amplitude, and phase such that electric energy is coupled back into a separate piezoelectric strain actuating element attached to the blade spring and shoe assembly effective to create a vibratory moment therein which counteracts and neutralizes the existing vibration of the blade spring and shoe assembly. The predetermined frequency or frequency band can correspond to a resonant one, but this embodiment is not limited to that situation. In one aspect, a voltage signal is fed back into the piezoelectric material of the piezoelectric strain actuator element causing a controlled vibratory moment and change in physical dimensions of the piezoelectric strain element sufficient to dissipate the vibration sensed in the blade spring and shoe assembly via the sensing element as an intervening component (as these components are all mechanically coupled together).
In addition, in the active damping system, an amplifier can be used to increase the power of the feedback voltage signal generated by the active control circuit of the control unit to afford more robust vibration control. The amplifier generally is connected to a power source, such as a battery source, in this embodiment. By appropriate selection of the vibration frequency to which the control unit responds as well as the characteristics of the feedback signals using the active control circuit, the piezoelectric strain actuating element can be used as a force actuator to effectively counteract a resonant or other forced vibration in the blade spring or shoe from not only chain-induced vibration but also other vibrational inputs originating from other locations in the engine or vehicle. This active dampening configuration of the invention permits the piezoelectric elements to reduce vibration over a broad frequency range or individual preselected frequencies.
In an alternative aspect of the active damping mode of the invention, the vibration sensor is an accelerometer or similar microelectromechanical motion sensor physically coupled directly to the blade spring and shoe assembly, or alternatively as remotely attached to some other engine or vehicle component having vibrational forces that are transferred at least in part to the chain. The accelerometer is coupled to the control unit in any convenient manner effective to supply data signals thereto (e.g., via wireless or wired coupling).
The piezoelectric damping systems of this invention, accordingly, dissipates vibration of the blade spring (or shoe) caused by the blade spring (or shoe) reacting to varying tension in the chain, such as imparted by tortional engine vibrations. In this way, the spring force of the blade spring is curbed from reacting to the tortional engine vibrations with a resonant or other type of vibration that otherwise might establish a prolonged oscillation of the chain. It will be appreciated that the coupling of a piezoelectric strain actuating element to either one of the shoe or blade spring to dampen vibrations therein effectively dampens vibration in the tensioner as a whole, since these parts are all mechanically coupled together.
As will be appreciated, the tensioners according to this invention are unique, integrated multifunctional electromechanical systems for tensioning chains. The chain tensioners of this invention have excellent tensioning and vibrational damping performance capabilities. In addition, the chain tensioners of this invention also offer potential cost savings as non-hydraulically based chain tensioning and vibration dampening systems. Depending on the application, the tensioner of this invention reduces, and may eliminate, the need for expensive tensioner wear face materials, reduces chain noise and potentially increases the overall life of the tensioner parts and the reliability of the engine systems using a blade spring chain tensioner system. Further, by taking up chain slack of the strands in engine timing applications with less vibration, the present invention reduces the chance for changes in the timing between the crankshaft and the camshaft as the chain wears and/or slackens.
In one aspect of a chain tensioner that can be passively or actively damped by the vibrational control arrangements according to this invention, a shoe is mounted at one end to a stationary support, and a blade spring is mechanically interlocked with the shoe, such that the shoe can be positioned to bear against, and maintain tension in, a chain strand. The chain tensioner is positioned along a length of chain between sprocket gears with the shoe contacting the chain from outside of the chain path and imparting tension to the strand by displacing the chain path to eliminate slack in the chain strand. The chain displacement begins, or increases, as the temperature of the tensioner increases, for example, from frictional contact with the chain moving across a surface of the shoe. During such contact, the chain contacting shoe will tend to become less rigid, and the load from the blade spring causes the shoe to assume a more arcuate shape with ends of the shoe forced inward toward one another such that the convex side of the shoe extends further into the span of the chain, and thereby increasing the tensioning force applied by the shoe to the chain. The tensioning process is reversible when the shoe cools and becomes more rigid, thereby reducing the curvature induced by the blade spring.